To start, clearly state that there are no reserves in your trade ad. On the first boss, turn on master looter during the fight. Don't ninja anything, since that might at least offer some reason for the action, but instead very slowly link items and demand rolls. Tell people to chill or get lives if they request group loot. Ignore any claims that people can't ninja thanks to the "able to use" need system.

Be sure use raid warning for normal communication, rather than limiting it to when you need full, immediate attention.

Above all, make sure you treat a 90-filled transmog run of a level 70 raid as if it were extremely serious.

There may still be items that you really want, but for some reason did not reserve. If these drop and you do not win them, do the following. First, ask somewhat nicely, but with little punctuation. When the person opens trade, feel a sense of urgency. Know this: they are trying to scam you. For example, if they put the wrong item in, cancel trade and begin to yell at them. Ignore their absurd claims of "full bags" or "mistakes", because that's just what a bitch would say. Speaking of which, be sure to call the person a bitch. Maybe add in other profanity, such as stating that you can't stand this shit or how it is all bullshit. For the sake of clarity, call them a ninja.

Of course you can't be all talk. At some point the player with the item you want may finally find it in their bags. Before that happens you should swear some more and drop the raid.

Finally, be sure to tell them that you're opening a ticket to report them for ninjaing. Be sure to have screenshots of your earlier conversations, so that the GMs know that you're serious.